March 2011 Chevy High Performance Q&A - Performance Q&A

Under Pressure Round II

The selection of posis on the market include disc-type clutch, cone-type clutch, the traditional locker, and newer air lockers. The factory posi that GM/Eaton designed back in the ’60s is the disc-type clutch, which we prefer. One of the major issues with the factory posi is the strength of the side and spider gears, but Moroso redesigned the GM posi back in the late ’70s, and it’s still hard to beat for strength and performance. The spider and axle gears are made from forged H-11 aircraft steel bar stock, and Moroso increased the friction disc count from the factory 18 to 22. Between this count change and the increased spring pressure on the clutch pack, the posi gives you a 100 percent increase in breakaway torque. Now for the downside: Moroso only offers the posi carrier in a four-series design. Also, they can be quite aggressive for street use. We had one in our El Camino for 10 years and it will give you a good deal of chatter when turning slow-speed corners when the diff gets hot. If you stay up on the gear oil with friction modifiers added, you can minimize this issue. The bottom line is you’re not going to break this posi! The Brute Strength posi is sold under PN 83000, and the Moroso Climbing gear lube is PN 34800you can also check out the GM Posi Lube PN 1052271

To find a gear ratio that works for you, check out Precision Gear, which offers a 3.73:1 gearset (PN GM12/373C, specifically designed to work on a four-series case. This gives you a gear range from 3.73:1-6.10:1 on a four-series case. Precision also offers specialty gears that allow you to use 4.10s and 4.56s directly onto a three-series carrier without the above-mentioned blanchard ground spacer. CHP
Sources: moroso.com, precisiongear.com

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